This invention relates generally to food heating units, and more particularly to a counter-top unit which is usable in homes and offices and is adapted rapidly to reheat a stack of such packages containing pre-cooked food in a cold state to a service temperature level and to maintain the food at this level for an indefinite period.
To satisfy the growing need for quickly prepared inexpensive meals, convenience food systems have been developed in which the meals to be later served are first cooked, packaged, and then deep-freezed. When one wishes to eat a particular meal, the selected package is taken out of the freezer and the frozen pre-cooked meal is then thawed and reheated. Typical of such operations is the so-called TV dinner in which a pre-cooked meal in the frozen state is sealed within a serving tray. The dinner is kept in the freezer until a demand therefor arises, at which point the TV dinner is thawed and reheated in a microwave oven, a convection oven or whatever heater unit is available. The term "packages" as used herein is intended to cover any sealed dish, tray, pouch or other hard or soft container having pre-cooked food therein.
In reheating a pre-cooked frozen meal in homes and offices, it is difficult when going from the cold state to a service level in a conventional hot air oven, to avoid a situation in which the core of the metal is still cold even though the outer layer is hot. And when one seeks to ensure that the body of the food is hot throughout, there is a tendency to overheat the meal in the oven and thereby re-cook it, with a resultant loss in nutritional value and flavor. But even when the meal has been heated to a proper serving level, it must be served without delay, for with the typical oven it is virtually impossible to thereafter hold the meal at this level until such time as there is a demand therefor.
For a convenience food operation to be effective, one must be able to reheat the pre-cooked meal to a proper service temperature level within a relatively short period, taking into account that in a home and office, the time at which diners are ready to eat may be subject to change. Thus in a typical office having several staff members, all of whom intend to lunch at, say, noon, it is not at all unusual for one or more of the members to be unavailable until, say, an hour or so later. Existing ovens for reheating precooked frozen meals cannot cope with this common contingency.
In my copending application Ser. No. 277,027, whose entire disclosure is incorporated herein by reference, there is disclosed a counter-top unit usable in homes and offices for reheating packages containing precooked meals whereby the packages are rapidly brought from the cold or frozen state to a service temperature level and thereafter maintained indefinitely at this level without overheating and recooking.
The counter top unit disclosed in my prior application includes a case having an apertured partition therein to form a compartment, accessible from the front of the case for accommodating a stack of food packages with air-flow spaces therebetween. The compartment is spaced from the rear of the case to define a plenum and from the front to define an air curtain passage communicating with upper and lower air passages leading to the plenum. In operation, air drawn from the upper passage is heated and blown into the plenum to create a pressure differential between the plenum and the compartment, as a result of which the heated air is forced through the partition into the spaces between the packages to heat the food therein, the heated air also flowing in a continuous loop about the compartment through the passages to thermally isolate the compartment.
In the heat-up phase, the heated air is in the form of pulsatory wave in which the pulses are at a temperature above the service level, these pulses being separated by lower temperature intervals during which heat from the outer layer of the food is transferred into the body thereof to prevent the food from being heated above the service level. In the subsequent service phase, the temperature of the air is held at the service temperature level.
Heat is provided in this counter-top unit by high-wattage and low-wattage electrical resistance elements, both of which are energized in the heat-up phase to provide the required high temperature. However, in the heat-up phase, the operation of the high-wattage element is periodically interrupted whereby the meals are then subjected to pulses of high temperature air separated by relatively low temperature intervals during which heat from the outer layer of food is transferred to the intermediate layers and the core thereof to prevent the outer layer from being heated above the service temperature. When the body of the meals reaches the service temperature level, the unit switches over to a service phase in which only the low-wattage heater element is energized and thermostatically-controlled to maintain the food at the service temperature level for an indefinite period.
The practical problem with my prior arrangement for producing a pulsatory hot air wave is that when electrical resistance heater elements are used, even after the energization current is interrupted, residual heat retained by the element continues to heat the air passing thereover. Hence with relatively rapid pulse rates, it is difficult to obtain well-defined hot air pulses; for in some instances, the amount of heat in the intervals between pulses is excessive.